For just $100, I've got an opportunity to purchase a used Lennox natural gas heater for my new detached shop build-out. The shop in question is an open, three-car garage, approximately 1,100 square feet with open attic access (which I will be sealing with a drywall ceiling and insulation above that). The shop is located in the PNW, not a very cold climate but this time of year it does get to 30-40 degrees F on a regular basis. This heater looks to be 75,000 BTUs and 80% efficient which should work fine for my space... It may even be a bit on the large end but advice I've received tells me this BTU range would be a good fit. I was removed from a home because the owners were converting the garage to a living area and doing some further renovation work; I've been told it was working at the time it was removed. It has been in garage storage for about a year.

I've been looking at natural gas shop heaters but new, they're around $750 and when you add venting, the total cost can easily climb over $1,250. I'm already going to take a hit of $500 for the utility to run a second gas line to the shop and install a meter on the side of the shop (which is a subsidized cost, quite a deal actually).

My actual question - what's your feeling on using a whole-house heater like this, for just the garage? I see it does have a horizontal attic mounting option which might work for my application. For $100, I'm willing to spend a little more time on a custom install. I'd like to keep it in the attic or along the ceiling so it doesn't obstruct floor space, but if I need to build a cabinet for it, that's fine too. It's not very large (about 3x3x2 feet).

Will the costs of venting be more than a standard garage heater (which I think is usually a 6" diameter tube)? Are there any other costs/accessories I need to account for? The instruction manual shows a Cooling Coil, Electronic Air Cleaner and Automatic Humidifier used in the horizontal attic installation -- are these required or optional?

Not sure if this is a concern, maybe others will know, but if you are doing finishing in this area and this heater has an open flame would that be an issue if the heater draws combustion air from the room. It could potentially draw in fumes that could be ignited in the right mixture.

I know the Modine Hot Dawg heaters have a model that has a closed combustion chamber and use outside air. I think they would be safer IF you were using finishing materials where an open flame would be prohibited. You could of course not operate the heater during these times when you are applying finish.

I don't know the answer just asking the question I would have if I was considering installing a heater such as this in my shop.

Not sure if this is a concern, maybe others will know, but if you are doing finishing in this area and this heater has an open flame would that be an issue if the heater draws combustion air from the room. It could potentially draw in fumes that could be ignited in the right mixture.

Bob, good point and that is a benefit of newer garage heaters with concentric venting and the ability to exclusively pull in air from the outside for combustion. Not sure if I could rig this to work in that way or not, but I won't be doing a whole lot of finishing. If anything I may occasionally use my HVLP gun to spray some cabinets, but I'm thinking about isolating that finishing room and actually not heating it, or having a vent where I can opt to heat the room or close it off.

My neighbor moves houses at a relatively slow but steady rate. Every house he moves, he strips the HVAC system from the house and installs it in one of the many outbuildings he owns. So in Minnesota all of his outbuildings have heat and AC. A rather nice luxury. What he pays for this luxury is however, another question.

When we installed a completely new HVAC system in our house (2 years ago), we saved about $20 per month on the heat and saved about $80-100 per month on the AC.

There’s nothing wrong with installing a house furnace in a garage, it’s rather about the efficiency of the furnace you install and the average number of heating days in your local area.

My neighbor leaves his temp setting in the garage to 45 degrees, just enough to melt the snow off his car and yet enough to keep the the moisture from rusting his tools, and within 30 minutes, he can bring the temp of the garage up to 60 degrees. I’m planning on building a 3 car garage this spring but am conflicted as to whether to implement in floor heating or just a cheap second hand furnace. They both have their pluses.

Of course the gas company wants to install a second meter. They will charge you $5.00 a month for that option. If you want the gas turned off during the summer they will also charge you a re-connection fee. Might be worth asking them to install a tee at the house and pipe it over after the currently installed meter. Most any plumber could also handle the task, and depending on code, location, etc. you could trench for the gas line ahead of time to save money.

You may want to check the local building codes. I was looking into putting a gas furnace taken from a house in my detached 2-car garage, and was told that the utility wouldn't hook up the unit without a back-draft damper, a requirement for a furnace in a garage. My argument that it was a wood shop didn't count - if it had a roll-up door, it was a garage.

In-floor and radiant heating systems both recover rather quickly compared to heated air systems. I had a heated air system in our last house (80,000 btu hanging warehouse furnace) and it could recover to 60 degrees in about 10-15 minutes on a below zero day. I actually hung a 5,000 watt electric unit today in the shop off of our unheated garage in our current house. Another hanging furnace will be sourced for this garage over the summer. I need to insulate and drywall first.

I’m a big supporter of in-floor heat for garages. However, once that garage door is opened and all that heat escapes, how long does it take to get that living space back up to temp?

I wouldn’t worry about it unless you’re constantly opening and closing the doors or leaving them open. When moving a single car in or out of the garage, my minisplit ramps up for less than 5 mins to recover, but as long as the objects in the space are already up to temp, the recovery is minor. If you were really concerned, you could provision a small 220v electric heater just for this purpose. You’ll never get another chance to put the in floor heat and it’s a whole different level of comfort, don’t let that recovery scare you.

I thought about using a high efficiency furnace for my pole barn, but ultimately went with a ceiling mount shop heater because my hvac guy told me that if used an h.e. furnace I would have to winterize it if I didn't keep the temp above freezing all the time. Depending on the design apparently condensate can freeze and either break things or keep the furnace from starting if it doesn't break anything.

My shop is in an outbuilding the size of a two car garage which I built some 30 odd years ago. And every winter I kick myself for not putting heating coils in the concrete. Even with the shop toasty warm, that concrete is always cold. If only I could do it all over......

My current workshop, our 2 car garage that only my wife parks in, I have a vented kerosene monitor heating that and when we have a lot of days like this year with wind and temps in the 20’s I go through about 7-10 gallons per week, even with it set around 58 degrees. Shortly I have a 1,200 sq ft pole building being put up for my dedicated work shop. A friend of mine who does hvac recommended that I install 2- 1.5 ton mini splits which he says is the cheapest and most efficient way for me to go. So luckily I get a discount through him, and my son knows how to hook them up and get it going, I just need to do the electrical. The cost is just under $2,000. Everyone insists how efficient the mini splits are, which I do believe. I still plan on installing a wood/coal stove just to keep the draw from the electric overnight, and it’s a good way to get rid of my scrap. I don’t see anything wrong with using any type of unit that was taken out of your house or someone else’s to use in a garage or workshop.

I wouldn’t worry about it unless you’re constantly opening and closing the doors or leaving them open. When moving a single car in or out of the garage, my minisplit ramps up for less than 5 mins to recover, but as long as the objects in the space are already up to temp, the recovery is minor. If you were really concerned, you could provision a small 220v electric heater just for this purpose. You’ll never get another chance to put the in floor heat and it’s a whole different level of comfort, don’t let that recovery scare you.

Thanks for the input... that's good to know. I didn't want to install in-floor heat only to have to mount a Reznor to the ceiling also.

Of course the gas company wants to install a second meter. They will charge you $5.00 a month for that option. If you want the gas turned off during the summer they will also charge you a re-connection fee. Might be worth asking them to install a tee at the house and pipe it over after the currently installed meter. Most any plumber could also handle the task, and depending on code, location, etc. you could trench for the gas line ahead of time to save money.

Yeah, I know about the additional meter charge. Problem is, the main residence gas meter is on the opposite end of the house, and I'd have to cut through a lot of asphalt to make the tee. It's worth the extra $5 a month or whatever to just have the utility run a new meter from the street and avoid all that. Really I'm quite lucky they were willing to do a "subsidized install" as I've heard many utilities won't do that for a second line on the same plat. Was chatting with an old coworker the other day with a large detached shop and his utility quoted him in excess of $30K just to run the gas lines and add a meter. He pays over $100 a month to heat his garage with electric right now.